Vehicles having height adjustable air suspension systems are well known and commonly used. Generally, such systems include a plurality of air springs compressibly supported between the sprung and unsprung masses of the vehicle. The air springs are commonly positioned adjacent each wheel of the vehicle. On a passenger vehicle, for example, each wheel is supported on the frame or unsprung mass of the vehicle by a pivot arm, and an air spring and damper arrangement is typically supported between each pivot arm and the body or sprung mass of the vehicle. The height of the passenger vehicle can then be adjusted on a wheel-by-wheel basis by delivering or exhausting a quantity of air into or out of each air spring to respectively increase or decrease the height of the same, which in turn adjusts the height of the vehicle. As such, the operator can adjust certain performance characteristics of the vehicle as desired. For example, the amount of ground clearance can be increased where rough terrain is encountered, or the center of gravity can be lowered to improve handling during high speed driving. To help ensure that each air spring is at the desired height, such suspension systems often include a height sensor adjacent each air spring and damper arrangement.
Given the prevalence of these height adjustable suspensions systems, additional features have been added to these types of suspension systems in recent years to permit the same to provide dynamic leveling of the vehicle while the same is in operation. Such systems are used to compensate for body roll and other movements. However, one disadvantage of such systems is that adjusting the level of the vehicle while the same is being accelerated or decelerated, such as when the vehicle is traveling through a turn, when the vehicle is undergoing a braking action and/or when the vehicle is increasing speed, for example, can result in the vehicle having unusual or uneven height conditions that can unfavorably affect handling. As such, these systems tend to be sophisticated to avoid and/or compensate for such conditions.
One example of such a system is disclosed in Raad, et al. (U.S. Pat. No. 5,430,647). Raad discloses a system and apparatus for maintaining vehicle ride height by using height sensors at each wheel to measure the relative height of the body at each wheel. The system then identifies differences in ride height from side to side and from front to back, and acts to adjust the vehicle ride height to compensate for the body movements. As mentioned above, one disadvantage of such systems is that the same are complex and often require sophisticated sensing and computational systems to attempt continually to measure and compensate for dynamic body movements of the vehicle.
Another disadvantage of systems such as that disclosed in Raad, for example, is that the continual adjustments of the suspension system to compensate for the dynamic movements of the body of the vehicle tend to consume a considerable amount of compressed air. As such, the power consumption of the compressor supplying the compressed air can be significant. Techniques have been used in attempts to reduce the compressed air consumption and attendant power load. One such technique includes monitoring the braking system and not leveling the suspension system while the braking system is in operation. This technique, however, also has disadvantages. One such disadvantage is that the braking system typically operates for only a fraction of the time that the vehicle is in operation. As such, this technique often provides only minimal reduction in compressed air consumption and power usage.
Another disadvantage of such systems is that there are other conditions during the dynamic operation of the vehicle in which it is desirable to avoid leveling or otherwise adjusting the suspension system of the vehicle. These conditions can include when a vehicle is accelerating, such as laterally, longitudinally or in a resultant direction, for example. To date, however, known systems have not determined whether or not conditions are appropriate for leveling a vehicle based, at least in part, on an acceleration level of the vehicle.